The present application claims priority to Japanese Application No. P10-263695 filed Sep. 17, 1998 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a magnetic tunnelling element in which a pair of magnetic layers are laminated via a tunnel barrier layer and in which the tunnel current flows from one to the other magnetic layer, with the conductance of the tunnel current being changed in dependence upon the relative angle of magnetization of the paired magnetic layers. This invention also relates to a method for manufacturing the magnetic tunnelling element.
2. Description of the Related Art
It has been reported that, if, in a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers, a pre-set voltage is applied across the paired magnetic metal layers as electrodes, a magnetic tunnelling effect is produced, in which the conductance of the tunnel current flowing through the insulating layer is changed in dependence upon the relative angle of magnetization of the paired magnetic metal layers. That is, a layered structure comprised of a thin insulating layer sandwiched between a pair of magnetic metal layers exhibits a magnetoresistance effect with respect to the tunnel current flowing through the insulating layer.
In this magnetic tunnelling effect, the specific magnetoresistance ratio can be theoretically calculated based on the spin of polarization of the paired magnetic metal layers. In particular, if Fe is used as the material of the paired magnetic metal layers, expectation may be made of the specific magnetoresistance ratio of approximately 40%.
Therefore, a magnetic tunnelling element having a layered structure comprised of a thin insulating layer sandwiched between paired magnetic metal layers is stirring up notice as an element for detecting an external magnetic field.
In the above-described magnetic tunnelling element, an oxidized metal is usually used as the thin insulating layer. However, if a metal oxide is used as an insulating layer, pinholes etc tend to be formed, such that short circuit tends to be induced between the paired magnetic metal layers. There are occasions wherein, if a metal oxide is used as an insulating layer, the metal oxidation degree is insufficient, such that the tunnel barrier is incomplete and the magnetic tunnelling effect is not showed.
It is therefore an object of the present invention to provide a magnetic tunnelling element through which the tunnel current flows positively in the insulating layer to exhibit the magnetic tunnelling effect in stability.
In one aspect, the present invention provides a magnetic tunnelling element including a first magnetic layer, a tunnel barrier layer formed on the first. magnetic layer, and a second magnetic layer formed on the tunnel barrier layer. The tunnel barrier layer is formed by oxidization of a metal film using an inductively coupled oxygen plasma.
The magnetic tunnelling element according to the present invention has a tunnel barrier layer which is formed by oxidization of a metal film using an inductively coupled oxygen plasma. Thus, the tunnel barrier layer is able to insulate the first magnetic layer reliably from the second magnetic layer in a manner free from defects.
In another one aspect, the present invention provides a method for manufacturing a magnetic tunnelling element including forming a first magnetic layer, oxidizing a metal film by an inductively coupled oxygen plasma for forming a tunnel barrier layer on the first magnetic layer, and forming a second magnetic layer on the first magnetic layer via the tunnel barrier layer.
In the manufacturing method for the magnetic tunnelling element according to the present invention, the metal layer is an inductively coupled oxygen plasma, in forming the tunnel barrier layer. Thus, with this technique, the metal layer can be oxidized without sputtering. Therefore, with this technique, the tunnel barrier layer can be formed which is able to insulate the first magnetic layer reliably from the second magnetic layer without damaging the metal film.
In particular, with the magnetic tunnelling element according to the present invention, the metal film is oxidized with an inductively coupled oxygen plasma to form the tunnel barrier layer. Thus, with the present magnetic tunnelling element, the first magnetic layer can be insulated reliably from the second magnetic layer without producing short circuit. Therefore, with the present magnetic tunnelling element, the tunnel current is allowed to flow reliably between the first and second magnetic films.
Also, with the manufacturing method for the magnetic tunnelling element according to the present invention, the tunnel barrier layer can be formed by oxidization of a metal film using an inductively coupled oxygen plasma. Thus, with the present technique, the tunnel barrier layer can be formed which reliably insulates the first magnetic layer from the second magnetic layer without damaging the metal film, so that it becomes possible to prevent malfunctions such as short circuit between the first magnetic layer and the second magnetic layer to improve the productivity significantly.